Magnetic recording media such as video tapes and audio tapes are required to have excellent electromagnetic conversion properties, running property and durability.
For satisfying the above requirements, various attempts have so far been tried.
For the purpose of improving all of the electromagnetic conversion properties, running property and durability, there is proposed a magnetic recording medium in Japanese Patent Publication Open to Public Inspection (hereinafter called JP O.P.I.) No. 60-93626/1985, in which a surface roughness R.sub.a (M) of a support surface on a magnetic layer side is controlled to not greater than 0.03 .mu.m; a surface roughness Ra(B) of a support surface opposite to the magnetic layer is controlled to 0.02 to 0.1 .mu.m; and R(M) and R(B) satisfy the following equation: R.sub.a (M) &lt;R.sub.a (B).
However, a waviness on a support surface deteriorates the electromagnetic conversion properties. If a support surface opposite to a magnetic layer is roughened by providing high protrusions thereon, the protrusions on a wound tape are liable to stick into a magnetic layer surface and roughen it; a dropout is caused by scraping-off of the high protrusions in manufacturing; and further, the high protrusions are scraped off while running in a deck and the fillers contained therein may damage the support surface to produce noises. Because of the above reasons, the electromagnetic conversion properties cannot always be improved even if the roughness of a support surface on a magnetic layer side is simply minimized.
On the contrary to the above, there is proposed a magnetic recording medium in JP 0.P.I. No. 57-150130/1982, in which the surface roughness of a support on a magnetic layer side is roughened more than that of the support surface opposite thereto in order to improve the electromagnetic conversion properties.
However, a very smooth support surface opposite to the magnetic layer is liable to cause troubles in transporting such as weaving or sticking in a calendering process.
Further, there are disclosed various recording media in JP O.P.I. 185224/1987 where .mu.K and Rrms of a magnetic layer are controlled to lower a head stain; in JP 0.P.I. 268118/1988 where a magnetic layer contains a binder comprising a vinyl chloride resin having a phosphoric acid group and a polymer having a functional group, and alumina having an average particle size of 0.1 to 0.3 .mu.m; and in JP 0.P.I. 275022/1988 where foregoing alumina is replaced with carbon black having an average particle size of 20 to 120 .mu.m.
However, mere control of .mu.K and Rrms of a magnetic layer involves such problems that head stain is not necessarily lowered and that the electromagnetic conversion properties are rather deteriorated and an abrasion of a magnetic head is increased.
Addition of alumina for elimination of head stain is liable to have a problem that head stain is inevibaly increased, and adding carbon black for solving the head stain problem is liable to inevitably result in deteriorating the electromagnetic conversion properties.
Further, any one of the above technologies are not suitable for improving dispersibility of a magnetic powder by treating the surfaces thereof with SiO.sub.2.
Further, there are proposed the magnetic recording media in JP O.P.I. 146129 to 146131/1989 where a magnetic layer contains a hydrate of metal oxide to reduce a rubbing noise; and in JP O.P.I. 77030/1983 where there is used a plastic film support having a specific contact angle with water to increase adhesiveness of a magnetic layer to a support.
The magnetic recording medium containing a metal oxide hydrate involves the problem that dispersibility of a coating solution for a magnetic layer is worsened, so that the electromagnetic conversion properties are deteriorated. Further, the magnetic recording medium comprising a plastic film support having the specific contact angle with water also has the problem that an additive to the plastic film is liable to deteriorate rigidity of the support, which in turn results in deteriorating a running property and a durability of the recording medium.